1. Field of the Invention
The invention relates to a method and arrangement for simultaneously displaying a graphic image and a video image, the graphic image being accommodated within a window. The invention also relates to a television receiver, a video recorder and a multimedia station comprising such an arrangement.
2. Description of the Related Art
A prior-art method of displaying a graphic image within a window of a video image is disclosed in UK Patent Application GB-A-2 242 594. To improve the visibility of the graphic image, the contrast of the video image is reduced within the window.
It is an object of the invention to further improve the prior-art arrangement.
In accordance with the invention, the method is characterized by generating a background color signal for said window and mixing said background colour signal and the video signal representing said video image. It is thereby achieved that the window can be given a color contrasting with the graphic image colour while maintaining the display of the video image within the window. The visibility of the graphic image is further improved by giving the window a background color. More particularly, the legibility of text constituting a menu-on-screen is considerably improved. moreover, the appearance of menus-on-screen is considerably enhanced. The window resembles a colored, partly transparent, piece of glass between the graphic image and the video image.
As described in the patent application mentioned above, the step of generating a background color signal is known per se. However, the video image is then not displayed within the window. The graphic image may have a perfect visibility, but a part of the video image is lost and cannot be observed. It is further known from international patent application WO 94/21080 to additively mix a graphic image with a video signal. However, it is not desirable that the video signal remains visible through the graphic image itself, e.g., through the characters of a menu.
To prevent the mixed signal within the window from assuming a too large amplitude, the video signal and the background color signal may be given weighting factors, for example, xcex1 and 1xe2x88x92xcex1, respectively. The larger the value of xcex1, the better the underlying video signal remains visible. The weighting factor xcex1 will therefore also be referred to as xe2x80x9ctransparencyxe2x80x9d of the window.
Experiments have shown that the legibility of on-screen-menus is substantially affected by the amount of activity in the video image. More particularly, video images having fine picture details with a high contrast (e.g., text) substantially interfere with graphic menus. Said interference occurs, in particular, when the video image is static. In a preferred embodiment of the invention, the weighting factors are therefore controlled in response to the amount of activity in the video image within the window. The amount of activity in the graphic image may be taken into account as well so as to determine when interference between video and graphic image details is most annoying.
It has also turned out that menus in television receivers have a different legibility for different categories (drama, documentaries, sports) of television programs. In a further embodiment of the invention, the weighting factors are therefore controlled in response to said categories.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.